Data is stored on magnetic media by writing on the magnetic media using a write head. Magnetic media can be formed in any number of ways, such as tape, floppy diskette, hard disk, or the like. Writing involves storing a data bit by utilizing magnetic flux to set the magnetic moment of a particular area on the magnetic media. The state of the magnetic moment is later read, using a read head, to retrieve the stored information.
Conventional thin film read heads employ magnetoresistive material, generally formed in a layered structure of magnetoresistive and non-magnetoresistive materials, to detect the magnetic moment of the bit on the media. A sensing current is passed through the magnetoresistive material to detect changes in the resistance of the material induced by the bits as the media is moved with respect to the read head.
The magnetoresistive effect, given by xcex94R/R, may be detected by passing a sensing current through the sensor along the plane of the layers, or by passing current through the sensor perpendicular to the plane of the layers. By passing the sensing current perpendicular rather than parallel to the plane, shunt current through non-magnetoresistive layers of the sensor can be eliminated, thus improving the magnetoresistive effect.
Current perpendicular-to-the-plane devices or CPP devices may have a giant magnetoresistive multilayer, a spin tunneling junction, a spin valve, or other stacked type sensor device. For example, U.S. Pat. No. 5,668,688, by Dykes et al., entitled CURRENT PERPENDICULAR-TO-THE-PLANE SPIN VALVE TYPE MAGNETORESISTIVE TRANSDUCER, issued on Sep. 16, 1997, herein incorporated by reference in its entirety, discloses a possible CPP device.
CPP devices while overcoming some problems associated with the current in the plane or CIP devices, have other design problems. For example, U.S. Patent entitled MAGNETORESISTIVE TRANSDUCER WITH FOUR-LEAD CONTACT, by David Richardson, et al., Ser. No. 09/006,307, filed on Jan. 13, 1998, issued as U.S. Pat. No. 5,959,811 on Sep. 28, 1999, herein incorporated by reference in its entirety, describes problems associated with providing electrical contacts to the magnetoresistive sensors. With CPP devices, because the thin film layers have such a low resistance perpendicular to their plane, the resistance of the sensing leads significantly reduces the magnetoresistive effect of the device. Thus, it is important to minimize the resistance of the leads. As such, the leads typically are formed of low resistance conductive materials, such as Au, Ag, Al, Cu, or the like.
Low resistance lead materials, on the other hand, have been observed by the present inventors to create another problem in CPP devices. Because the magnetoresistive stack typically is formed on the lead material, the lead material is partially etched when defining the magnetoresistive stack. This causes lead material to redeposit on the side walls of the magnetoresistive stack. This is particularly true at small geometries.
The redeposited lead material creates a shunt path around the layers which significantly reduces the magnetoresistive effect. Due to the smaller path length, such current shunting is even more detrimental in CPP devices than in than the current shunting that occurs along the layers of CIP devices. Thus, while low resistance leads are necessary for optimizing the magnetoresistive effect, their redeposition on the side wall can significantly reduce the magnetoresistive effect by providing a low resistance shunt path around the stack.
The preferred embodiments of the present invention provide an improved current perpendicular to the plane thin film read head device and method of fabrication. A current perpendicular to the plane or CPP sensor element is formed between upper and lower sensor lead structures which couple sensing current to the sensor element. With the preferred embodiments of the present invention, the lower lead is formed to inhibit accumulation of redeposited lead material on the side walls of the sensor element.
In the preferred embodiment, the lower lead is formed so that the upper portion of the lead, which normally is etched during sensor element formation, is formed of a low sputter yield material. This provides improved process control and reduces redeposition flux to the side walls of the sensor element thus reducing accumulation of redeposition on the side walls.
In addition, it is preferred to form the upper portion of the lower lead of a material that also has a low value for the sputter yield ratio of low milling angle-to-high milling angle for the milling angle selected to form the sensor element. In general, the sputter rate preferably should increase for milling angles from about 20 to 70 degrees. This allows a small milling angle, with respect to normal, to be used to define the sensor element. Because the sensor sidewall is generally perpendicular to the lead surface, the milling angle of the sensor sidewall is large when a small milling angle is used to form the sensor element. As such, the higher sputter rate at the high milling angle of the sidewall will inhibit accumulation of redeposited lead material on the sensor.
Using a smaller milling angle to define the sensor element improves processing characteristics and allows for more precise formation of a smaller sensor element. The present invention, therefore, allows for smaller track width devices, thus improving the aerial density of data storage and retrieval apparatuses.
In a preferred embodiment, conventional lead material is clad with a low sputter yield ratio material to form the lower lead to reduce the resistance of the lower lead structure. The cladding may have one or more layers of material. In this embodiment, the underlying lead material may be formed of conventional low resistance lead material such as Au, Ag, Cu, Al, or the like. Hence, the effective resistance of the clad lead is lower than a lead that is formed of only, or a large amount of, low sputter yield ratio material. As such, in one embodiment it is preferred to minimize the thickness of the cladding, while providing sufficient thickness to prevent etching of the underlying lead material.
Furthermore, although redeposition accumulation may be reduced by cladding only the portion of the lead material exposed to ion milling from low sputter ratio material, in the preferred embodiment, the sensor element is formed on the cladding. As such, it is preferred that the cladding material be a low sputter ratio material that also has low resistivity, to minimize lead resistance, thus optimizing the magnetoresistive effect. Refractory metals, such as tantalum, titanium, tungsten, molybdenum, zirconium, vanadium, niobium, their alloys, or the like are expected have desirable low sputter yield ratios and sufficiently low resistivity so as to not significantly reduce the magnetoresistive effect of the device.
In addition, as the cladding of preferred embodiments has a higher resistivity than typical lead materials, any sidewall redeposition that may occur will have higher resistivity than conventional sidewall deposition. Thus, even if some amount of redeposition does occur, preferred embodiments provide reduced shunt current in sidewall redeposition as compared to conventional lead material sidewall deposition.
The improved CPP read head may employ a giant magnetoresistive multilayer, a spin valve, a spin tunneling junction, or other known CPP stack type element. The improved CPP read head of the present invention may be embodied in a data storage and retrieval apparatus.